Motorcycle Forum banner

1 - 20 of 24 Posts

·
Registered
Joined
·
12 Posts
Discussion Starter #1
I start my cycle using the choke. As I push the choke in it starts to stall and I need to use the throttle to keep it running. Then I noticed I am leaking some gas underneath. Someone told me to use Sea Foam to unclog the carb? What do you recommend?
 

·
Premium Member
Joined
·
5,478 Posts
First, it is recommended you go to the New Member Introduction page to let us know something about you.

Second, how about telling us what bike year/make/model and any changes from stock. Also, a photo or diagram of just where the leak is would be very helpful.
 

·
Registered
Joined
·
12 Posts
Discussion Starter #4
First, it is recommended you go to the New Member Introduction page to let us know something about you.

Second, how about telling us what bike year/make/model and any changes from stock. Also, a photo or diagram of just where the leak is would be very helpful.
 

·
Registered
Joined
·
12 Posts
Discussion Starter #5
Can’t find new member introduction page. I have a 1981 Honda CB 500 Deluxe. It has under 10,000 miles and was running fine until about a week ago
 

·
Registered
Joined
·
26 Posts
Hi Howard,
To my knowledge, Honda did not produce a CB500 in 1981. Are you referring to the CX500 Deluxe? The sohc CB550 four cylinder bikes were discontinued in 1978. The CX is a V-twin with transverse cylinders and shaft drive.
As to your problem it sounds like your carbs could use some cleaning/maintenance. Check to see if the gas is leaking out of the overflow tubes which run down from the bottom of the carb bowls. If this is the case you probably have a stuck or dirty float needle. Try tapping on the float bowl to see if it will free up a sticky float. If that does not work you will have to drop the bowl and clean the needle/seat. Crap from the tank can get down in there and get stuck. You can sometimes drop the bowl, turn on the gas, and let some fuel run through the valve into a small cup and let it flush out the valve. Otherwise you can spray some carb cleaner in there and get it out.
Check this out first. If the gas is leaking from another point, then you will have to address that situation. Good luck.
 

·
Premium Member
Joined
·
5,478 Posts
OK, try this: New Member Introduction

The leak could be the carb overflow drain, which is a brass tube inside the float bowl, and, if the float valve doesn't close all the way, will try to keep the fuel from filling the cylinder. Sometimes, that tube will crack and keep the fuel level too low to keep the bike running. Is it a steady dribble whenever the petcock is on, or just from time to time?

I am fairly sure that carb has a real choke plate, and not the starting enricher newer ones have, so starting on choke will require you to support the idle until the engine is warm enough.
 

·
American Legion Rider
Joined
·
21,205 Posts
Thanks Rick (WintrSol)
 

·
Registered
Joined
·
26 Posts
OK, try this: New Member Introduction

The leak could be the carb overflow drain, which is a brass tube inside the float bowl, and, if the float valve doesn't close all the way, will try to keep the fuel from filling the cylinder. Sometimes, that tube will crack and keep the fuel level too low to keep the bike running. Is it a steady dribble whenever the petcock is on, or just from time to time?

I am fairly sure that carb has a real choke plate, and not the starting enricher newer ones have, so starting on choke will require you to support the idle until the engine is warm enough.
An excellent point, well done. I have had this happen as well. To test for this, remove the bowl and fill it with fuel to the top. Then observe for leaks. Don’t try to make this assessment visually as the cracks can be very difficult to detect by eye. Thanks Wintrsol.
 

·
Premium Member
Joined
·
5,478 Posts
Don't ask how I know about this one.:rolleyes: It's fairly rare, but if you are getting a steady dribble of gas, it is on the list.
 

·
Registered
Joined
·
12 Posts
Discussion Starter #13
I used some sea foam. The engine ran smoother, but I still had the gas leak and I still needed to keep the throttle slightly open.
 

·
Registered
Joined
·
12 Posts
Discussion Starter #14
Hi Howard,
To my knowledge, Honda did not produce a CB500 in 1981. Are you referring to the CX500 Deluxe? The sohc CB550 four cylinder bikes were discontinued in 1978. The CX is a V-twin with transverse cylinders and shaft drive.
As to your problem it sounds like your carbs could use some cleaning/maintenance. Check to see if the gas is leaking out of the overflow tubes which run down from the bottom of the carb bowls. If this is the case you probably have a stuck or dirty float needle. Try tapping on the float bowl to see if it will free up a sticky float. If that does not work you will have to drop the bowl and clean the needle/seat. Crap from the tank can get down in there and get stuck. You can sometimes drop the bowl, turn on the gas, and let some fuel run through the valve into a small cup and let it flush out the valve. Otherwise you can spray some carb cleaner in there and get it out.
Check this out first. If the gas is leaking from another point, then you will have to address that situation. Good luck.
You are correct. It is a CX 500 Deluxe with a shaft drive. Thanks for your input.
 

·
Premium Member
Joined
·
5,478 Posts
On the bottom of the carbs, there is a small cast tube, which is the overflow drain. Try to get a look at it, to see if that is where the fuel is leaking from. Also, is it a slow, intermittent drip, or a steady drip-drip-drip?
 

·
Registered
Joined
·
12 Posts
Discussion Starter #16
It is more of a steady drip only when I am running the engine. I think I told you I used Sea Foam to try to clean up the carb.
 

·
Premium Member
Joined
·
5,478 Posts
It is more of a steady drip only when I am running the engine.
OK, so it is likely coming from the overflow tube. That could mean a sticking float valve or sinking float, or that crack in the overflow tube. Since you have to hold the throttle to keep it running, and if this is also necessary after warming it up on a ride, an overfilled carb could be the culprit. Running SeaFoam, while a good idea, won't help if you have bits of stuff stuck in the float valve, or the float has leaked and doesn't float as high as it should. I think you are going to need someone familiar with carb operation take a look. If you are near enough to St. Louis, MO, I would have a look at it.
 

·
Registered
Joined
·
26 Posts
Good advice from WintrSol. The crack in the overflow tube is more prevalent in old Kehin carbs than you may believe. There are entire threads on the subject in some Honda forums.
As mentioned above, Seafoam won’t cure a stuck/leaky float or cracked tube. You must drop the float bowl to make the repair. On the bottom of the carb bowls there are rubber overflow tubes which run down behind the transmission to the ground. Pull these tubes, one at a time, off the bowls and see if the fuel is dripping out of the drain that you pulled the tube from. Then you will know for certain that this is where your leak is.
If the fuel is coming from the bowl drains, follow the advice mentioned above.
 

·
Registered
Joined
·
12 Posts
Discussion Starter #19
Thanks for the advice. I have a friend around the corner builds small block racing car engines in his garage. He has a fairly complete machine shop. He knows about carbs. I’ll let you know what happens.
 
1 - 20 of 24 Posts
Top